JavaScript Summary

Variables

counter = 0; ....; counter = counter+1; etc.

var step, n; // Declaring variables is optional, but it is a good idea, important in functions.

Numbers

Integers:	7, -7 etc.
Octal:	012	= 10₁₀
Hex:	0xff	= 255₁₀, useful for rgb colours
Floating Point:	314.0e-2 == 3.14

Strings

"a string" and 'another string'

NB. HTML uses " for strings, so in those places that HTML and JavaScript meet, JavaScript should use '.

\n newline, \t tab, \' quote, \" double quotes

Arrays, sparse

new Array( )	creates a new one
var a = new Array( )	declares an array variable
a[7]	7th element
a["fred"]	the fred element, equivalent to a.fred

Objects

new someObject( )	create a new one; can omit ( ) if no params
var o = new someObject
o.f	access field etc.

Functions

function fnName(param1, param2) { ... code ... }

return, return value, optionally can "drop out" the end of a fn

Operators

The JavaScript operators are drawn from C.

NB. + is numeric addition and also string concatenation

Being an interpreted "scripting" language, operands are converted to appropriate types for an operator if possible. This raises the question of whether "2"+"3" equals 5 or "23"? What do you think?

Equality == Note that strings are compared by value, not reference, c.f. C

typeof expression

returns "number", "string", "boolean", "object", "function" or "undefined".

Statements Assignment aVariable = anExpression; total += 2; // as in C Conditionals if(expression) statement if(expression) statement else statement Iteration for(start; test; change) statement for(variable in anObject) statement // runs through anObject's fields while(expression) statement break // quit a loop continue // next iteration of loop Compound Statement { statement₀ statement₁ ... } With with( anObject ) statement // anObject's fields become visible, c.f. Pascal re Functions return; return expression; // a result

Objects

User Defined Objects
function MyObject(p1, p2, ...) // constructor { this.f1 = p1; this.f2 = p2; ... } MyObject.prototype.f3 = someExpression; MyObject.prototype.f4 = someFunction; // etc.
// need `prototype' keyword as we are defining a class not an object instance

System Objects - some predefined JavaScript objects are listed here:
Array, e.g. new Array( ), var a = new Array(10), a.length==10, a.reverse( ), a.sort( ), arrays can be sparse and can "grow".
Boolean, wrapper class for boolean values.
Date, new Date( ), d.milliseconds (since 1/1/1970), d.getDate( ) (1..31), d.getSeconds( ), d.getMinutes( ), d.getHours( ), d.getDay( ) (0..6), d.getMonth( ) (0..11), d.getYear( ), and also d.setDate( ), ... etc.
Document // the HTML page in the Window

NB. document == window.document
document.applets[ ], document.applets.length
document.images[ ], document.images.length
document.URL
... etc.

Form

Button, b.form, b.name, b.value, b.type (=="button"), b.onclick( ) event handler.
Checkbox, ch.form, ch.name, ch.value, ch.type, ch.checked, ch.defaultChecked :boolean
Hidden
Option
...
Textarea

Frame, the sub-window objects of a window, see Window.
Function // a JavaScript function
History // the history of visited pages
Image // image in an HTML page
objects relevant to Java:

JavaClass // a Java Class for communication with applets
JavaObject // esp' applets
...

Link
Location // an URL, as in Window.location
Math // mathematical routines and constants

Math.E, Math.PI, ...
Math.cos( ), Math.acos( ), ...
Math.random( ) (result in [0.0 ... 1.0]), ...

MimeType
Navigator // the browser; it must annoy m.s.!
Number
Object // the empty object
Packages
String
Window // a frame or window of the browser

window.self, window.parent, window.top // the window/frame tree
window.frames[ ], window.frames.length
window.setTimeout(javascript-code, msecs-delay)
window.onload( ) window.onunload( ) // attributes set in HTML <BODY...> tag or <FRAMESET..> tag.

Security

Many attributes of JavaScript objects come under the protection of the security model. It is important that a JavaScript program in an HTML page and originating from a certain web site should not be able to discover all information about the user, the pages he or she has visited, data typed into forms etc. Such data are tainted and values computed from them are also tainted to prevent them from being misused, e.g. for "marketing" purposes.